How Long Is the Cannabis Vegetative Stage?

Quick answer

Indoor photoperiod cannabis plants veg for 3 to 6 weeks. Autoflowering plants veg for 2 to 4 weeks. Outdoor plants veg for 8 to 14 weeks in most US climates, from spring planting until daylight falls under about 14 hours.

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Vegetative stage defined

The vegetative stage starts when the seedling opens its first true leaves and ends when the plant starts to flower. During this phase the plant builds roots, stems, and fan leaves. It does not build buds yet. Light hours control the change in photoperiod plants. Age controls the change in autoflowers.

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Photoperiod plants

Most indoor growers keep lights at 18 hours on and 6 hours off, or 20 on and 4 off. The plant stays in veg as long as the dark period is shorter than 12 hours. A grower sets the length. Flip the timer to 12/12 and flower starts in 7 to 14 days.

When to Switch Cannabis Plants to Flower

A 3 week veg suits small tents and sea of green setups. A 5 to 6 week veg suits larger plants and training. Extra veg weeks add yield but also add height. Stretch in the first 3 weeks of flower can double plant height.

Autoflowering plants

Autoflowers flip to flower on a fixed clock, not on light hours. Most start flowering at 3 to 4 weeks from seed. The veg window is 2 to 4 weeks. Light stress or a small pot can shorten it. Autoflowers flower under any light schedule from 18/6 to 24/0.

Outdoor plants

Outdoor photoperiod plants track the sun. In the US, flowering starts in late July to late August as nights pass 10 to 11 hours. A plant set out in May vegs for 10 to 14 weeks. A plant set out in July vegs for 4 to 6 weeks. Latitude shifts these dates.

What changes the length

• Genetics: sativa leaning strains can stretch longer in veg.
• Pot size: a 3 gallon pot limits root space and plant size.
• Light: low light slows growth and adds weeks.
• Training: topping and low stress training add 1 to 2 weeks of veg.
• Temperature: cold rooms slow growth.

Signs the plant is ready to flip

1. Nodes alternate instead of sitting opposite each other.
2. Pre-flowers show at the nodes, with two white pistils on females.
3. Canopy fills about 50 to 70 percent of the grow space.
4. Plant height leaves room for stretch after the flip.